/*
Maximum Depth of Binary Tree
============================

Given the root of a binary tree, return its maximum depth.

A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Example 1:
Input: root = [3,9,20,null,null,15,7]
Output: 3

Example 2:
Input: root = [1,null,2]
Output: 2

Example 3:
Input: root = []
Output: 0

Example 4:
Input: root = [0]
Output: 1

Constraints:
The number of nodes in the tree is in the range [0, 104].
-100 <= Node.val <= 100
*/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */

class Solution
{
public:
  int maxDepth(TreeNode *root)
  {
    if (!root)
      return 0;
    int ans = 0;
    if (root->left)
      ans = max(ans, maxDepth(root->left));
    if (root->right)
      ans = max(ans, maxDepth(root->right));
    return ans + 1;
  }
};
